1. Field of the Invention
This invention relates generally to faceted gemstone construction and, specifically, to the faceted construction of a princess cut diamond, where said faceted construction provides improved luster and appearance.
2. Description of the Related Art
Diamonds have fascinated and beguiled mankind for thousands of years, yet the exact history of the precious stone is unknown. The word xe2x80x9cdiamondxe2x80x9d is derived from an ancient Greek verb meaning xe2x80x9cI tamexe2x80x9d or xe2x80x9cI subduexe2x80x9d. The ancient Greeks used this word for the hardest substance known, but it is difficult to tell what that substance was at that point in timexe2x80x94some believe the ancient Greeks may have been referring to the second hardest mineral, corundum (the gem variety of corundum is sapphire). Tracing the history of diamonds is complicated by this ambiguity with names.
The first diamonds were probably discovered around 800 BCE in riverbeds in India, and these alluvial deposits were rich enough to supply most of the world""s supply until the eighteenth century, when India""s dwindling supply probably spurred the exploration that led to the discovery of diamonds in Brazil, which became the next most important diamond source. In 1866, South Africa""s massive diamond deposits were discovered, and a world-wide diamond rush was on. Currently, western Canada is the site of the world""s newest diamond rush.
The cutting of diamonds into the complex formatted shapes we now associate with gems is a relatively recent practice. Although polishing and grinding with diamond dust was known from the thirteenth century, the first reference to diamond cutting is in 1550 in Antwerp, the most important diamond center of the period. Before the 1900""s, the various shaped cuts of diamonds, such as the Table Cut, the Old Single Cut, the Rose Cut, and the European or Old Mine cut, varied widely in appearance. Because of the limitations of technology, these diamonds had very small tables, large culets, and short pavilion facets (definitions of these below); but there was no single widely-recognized or agreed-upon standard of cutting them. Until recently, a unified science and theory of facet proportion did not truly exist.
In 1919, diamond cutter Marcel Tolkowsky wrote a doctoral dissertation that essentially established the modern standard of a xe2x80x9cbrilliant-cutxe2x80x9d diamond. Using only his own visual assessments of different variations of diamond cuts, Tolkowsky posited a theory of what cutting angles would produce the most proportionate balance of brilliance, scintillation, and dispersion in a gem-quality diamond. His measurements for achieving this balance were exact and strict. Fortuitously, improved cutting techniques and technology were being developed at the same time that finally allowed cutters to achieve more precise and stream-lined designs. Since that time, Tolkowsky""s measurements have evolved into the looser xe2x80x9cIdeal Cutxe2x80x9d standard promulgated by the American Gem Society (AGS).
The round brilliant-cut diamond sets the standard for all other diamond shapes, and accounts for more than 75% of diamonds sold today. The xe2x80x9cIdeal Cutxe2x80x9d brilliant-cut diamond has 58 facets (or 57, if there is no culet), which are broken down as shown in FIGS. 1A (side view), 1B (top view), and 1C (bottom view). The terminology used for describing the parts of the brilliant-cut diamond is used for describing the basic components of all the cuts of diamonds.
As shown in the brilliant-cut diamond profile of FIG. 1A, there are three basic sections to a diamond: the crown 110, the girdle 120, and the pavilion 130. The girdle 120 is the narrow rim of the gemstone that separates the crown 110 from the pavilion 130. It is the section with the largest diameter of any part of the stone. Usually it is left in an unpolished state with a matte finish. However, to achieve more overall brilliance (described below), girdle 120 is often ground. Crown 110 and pavilion 130 can be understood as the xe2x80x9ctopxe2x80x9d and xe2x80x9cbottomxe2x80x9d, respectively, of the brilliant-cut diamond. The tiny facet on the pointed bottom of pavilion 130 is the culet 135. The large, flat top facet of crown 110 is the table 115.
As shown in the top view of FIG. 1B, the brilliant-cut diamond has 16 Upper Girdle facets 111, 8 Star facets 112, 8 Bezel facets 113, and 1 Table facet 115 in the crown 110, which totals 33 crown facets in all. As shown in the bottom view of FIG. 1C, the brilliant-cut diamond has 16 Lower Girdle facets 131, 8 Main Pavilion facets 132, and 1 culet 135 in the pavilion 130, which totals 24 pavilion facets in all. The culet 135 is merely the point at the bottom tip of pavilion 130, although the culet may sometimes be much larger. As seen from FIGS. 1A, 1B, and 1C, as well as Tables 1A and 1B below, the brilliant-cut diamond has 58 facets. These facets are further described in Tables 1A and 1B by the angle each of their flat planar surfaces form with a the horizontal plane of girdle 120.
There are certain dimensional characteristics of a any gemstone that are useful for ascertaining its overall value. Many of these characteristics are based in the proportions the various parts of the gemstone have to the overall width of the gemstone. Using the brilliant-cut diamond in FIG. 1A as an example, the crown height (or crown height percentage) is calculated by dividing the height of the crown 150 by the overall width 160 of the diamond. The table percentage (or table) is calculated by dividing the table""s width 170 by the overall width 160 of the diamond. A table that is too large or too small will reduce the overall dispersion of a diamond""s brilliance (these qualities will be described below). The depth percentage (or depth) is calculated as the ratio of the overall depth 180 of the diamond by the overall width 160 of the diamond. A depth that is too shallow or too deep will allow light to escape through the bottom of the stone, reducing the stone""s overall brilliance and dispersion.
These various characteristics will be defined and described differently, depending on the type and shape of the stone being discussed. For example, the xe2x80x9cIdeal Cutxe2x80x9d characteristics of a brilliant-cut diamond are listed in Table 1C below.
The features that describe the optical beauty of a diamond are: brilliance, dispersion, and scintillation. For a cut diamond, a feature of primary importance is its brilliance, which is essentially how much it shines. A diamond has a refractive index of 2.42, which is a very high value compared with that of other jewels (the index of crystal is 1.55; rubies and sapphires, 1.77). As a result (using the brilliant-cut diamond of FIG. 1A as an example), when rays of light incident on table 115 reach pavilion 130, most of the rays are reflected totally (i.e., the rays of light do not escape the diamond through pavilion 130, but are reflected inward again), and escape upon reaching crown 110, thereby reaching the observer""s eyes as brilliance. The angles 131, 132, and 135 of pavilion 130 are important to total reflection, and thusly is important to the brilliance of a diamond.
The refractive index of the diamond also gives rise to the dispersion of the totally reflected rays of light into the seven colors of the visible light spectrum. This rainbow effect is sometimes called the fire of the stone. Scintillation is the glittering of the reflected light of a diamond caused by the movement of either the observer or the diamond itself. Scintillation depends primarily on the size of the diamond, the number of facets, the polish of the facets, and the accuracy of the angles of the respective facets. These features are somewhat subjective, and sometimes include luster, which is the quantity and quality of light reflecting from the surface of a diamond.
Diamonds are commonly assessed in terms of the xe2x80x9c4 Csxe2x80x9d: Cut, Clarity, Color, and Carat. Cut refers to both the geometric proportions of a gemstone and the final form into which the rough stone is shaped. The most prominent cuts in the industry are the brilliant-cut and the fancy shapes (which will be discussed more fully below). A good cut gives a diamond its brilliance, dispersion, and scintillation, in short, its appearance and appeal. Clarity is the measure by which a diamond is graded for purity, or whiteness. This is done by taking in the presence or absence of blemishes on the diamond""s surface, or inclusions within the diamond. The professional grading scale is: flawless (F); internally flawless (IF); very, very slightly included (VV); very slightly included (VS); slightly included (SI); imperfect (I).
Color refers to the system of grading diamonds on the quality of their tint, from colorless to a pronounced yellow hue. Modern methods use letters to designate differences in colors. They are D-F, for colorless; G-J, for nearly colorless; K-M, for faintly yellow; N-R, for very light yellow; S-X, for light yellow; Y-Z, for yellow. The traditional method ascribes names to the variations in tint: pure white (extra river; river), top-white (wesselton), off-white (silver cape, tope cape, cape, dark cape), yellow, and brown. Carat is the unit of weight (equal to 200 milligrams) by which a diamond or other gemstone is measured. The word is derived from the carob bean, whose consistent weight was historically used to measure gemstones.
In the latter part of the last century, the fancy shape (or fancy cut) diamond cuts have proliferated. The fancy shape cuts include the oval, the marquise, the pear, the heart, the emerald, the princess, the trilliant, and the radiant. Some of the fancy shapes are better suited for retaining the maximum weight of the more flat forms of diamond rough (called macles or flats), and many are also cut from the less perfectly shapped octahedral and dodecahedral crystals. However, unlike the brilliant-cut diamond, the specific proportions that make up the xe2x80x9cIdeal Cutxe2x80x9d of most of the fancy shape diamonds have not been conclusively determined or published by either the AGS or the Gemological Institute of America (GIA). It is known that AGS is currently working on a classification standard for fancy cut gemstones.
The present invention is primarily directed to a princess cut diamond. As discussed above, the xe2x80x9cidealxe2x80x9d proportions of this basically rectangular-shaped diamond do not have an industry-standard definition like the xe2x80x9cIdeal Cutxe2x80x9d proportions of the brilliant-cut (or other basically round-shaped) diamonds. A round diamond has a consistent pavilion angle that makes ideal proportions easier to establish as a depth percentage. A princess cut diamond has a pavilion that is made up of a variety of angles due to the unique pavilion shape and the variance in length and width.
A conventional princess cut diamond (sometimes referred to as a xe2x80x9csquare/rectangular modified brilliantxe2x80x9d in GIA grading reports) is shown in FIGS. 2A and 2B. FIG. 2A is the top view of the crown; and FIG. 2B is the bottom view of the pavilion. Although this particular princess cut diamond is shown as square-shaped, the princess cut can be rectangle-shaped. In FIG. 2A, the crown has a total of 25 facets. There are 4 upper girdle facets 210 (right above the girdle), 4 bezel facets 220, 8 triangular star facets 230, and 4 triangular crown facets 240. In addition, there is one table facet 250 comprised of a 8-sided polygon, thus creating a total of 21 facets. These facets are listed in Table 2A. Please note that the angles are not listed, because there are no industry-standard ranges for these values.
FIG. 2B is the view of the pavilion from the bottom of the conventional princess cut diamond. The pavilion has a total of 24 facets. There are 4 lower girdle facets 260 (located directly under the girdle). Making up the portions of the star-shaped sections of the pavilion are the 8 outer pavilion facets 270, the 8 inner pavilion facets, and the 4 main pavilion facets 290. The pavilion facets of the convention princess cut diamond are listed in Table 2B. Thus, combined with the 4 girdle facets (not shown in FIGS. 2A and 2B), the crown and pavilion facets make a total of 49 facets (50 facets if a culet is made/counted). Typical princess cut diamonds are either 50 facets or 58 facets (21 crown facets, 4 girdle facets, and 33 pavilion facets, including culet).
As was indicated above, the characteristic proportions of the princess cut diamond are measured differently, and have different effects than, similar proportions of a brilliant-cut diamond. Like the brilliant-cut diamond, the crown height, table percentage, and depth percentage are all measured using the overall width of the diamond (at the girdle); however, because the princess cut may take on a rectangular shape (viewed from the top, like FIG. 2A), the xe2x80x9cwidthxe2x80x9d needs to be defined. If the right and left sides of the princess cut in FIG. 2A were longer than the top and bottom sides, the longer distance (from top to bottom) would be the length, and the shorter distance (from side to side) would be the width. The longer length measurement is not taken into consideration when calculating overall width.
The longer length measurement is taken into consideration in one of the more important characteristics of the princess cut diamond: the length-to-width ratio. The length-to-width ratio is determined by dividing the length measurement by the width measurement (on GIA reports, these distances are always calculated in hundredths of a millimeter). Length-to-width ratios in the range of 1:1 to 1.5:1 are considered better. The length-to-width ratio of a princess cut diamond is largely determined by the rough diamond crystal from which it is cut. When a rare fine quality diamond is cut by an experienced diamond cutter, the weight and value will never be sacrificed simply to change the diamond""s length-to-width ratio if it is within the range of 1:1 to 1.5:1.
The princess cut diamond has a unique shape that is becoming increasingly popular with women for its beauty as well as its unique design capabilities. It is the only truly rectangular diamond shape that has a superior brilliance to the emerald cut. The effect and appearance of a princess cut diamond can be varied by altering the depth percentage and length-to-width ratios. The conventional depth percentage for a princess cut is between 65% and 80%. When a princess cut diamond is cut shallower than 65%, a greater percentage of light leaks out through the pavilion. When a princess cut diamond is cut deeper than 80%, the diamond appears darker in the center due to the large amount of light refracting through and out the bottom of the diamond.
Princess cut diamonds that are closer to square in measurement (i.e., with a length-to-width ratio close to 1:1) are typically more brilliant if the depth percentage is within a range of 65% to 75%. Princess cut diamonds with more rectangular shapes typically exhibit greater brilliance with depth percentages in the range of 70% to 80%. A summary of the typical values for a princess cut diamond are shown in Table 2C below.
In the more well-established field of brilliant-cut (i.e, round) diamonds, diamond cutters have sought ways to increase the brilliance of the brilliant-cut diamond by exceeding the xe2x80x9cIdeal Cutxe2x80x9d 58 facets. For example, Huisman et al. (U.S. Pat. No. 3,286,486) took the xe2x80x9cconventional twenty-four [pavilion] facetsxe2x80x9d of the brilliant-cut diamond and tripled them to create a pavilion with seventy-two facets. The greatly increased number of facets in the pavilion and the different angles at which a great many of them are cut result in enhanced brilliance. Nevertheless, Huisman et al. left the girdle and crown to be xe2x80x9cof any conventional sizexe2x80x9d. A later patent by the same inventors increased the number of facets of the girdle (Huisman et al. (U.S. Pat. No. 3,585,764)).
Other diamond cutters concentrated on other features besides brilliance. For example, Freiesleben (U.S. Pat. No. 5,657,647) reduces the number of crown facets in order to create large planar surfaces on the top of the diamond in order to xe2x80x9ccreate an impression of calm and hardnessxe2x80x9d. One diamond cutter sought to create greater dispersion (and the capability of highlighting colors) by etching fine grooves (0.1 xcexcm to 1,000 xcexcm) into the planar surfaces of the facets (Nakama (U.S. Pat. No. 5,612,102)). Another diamond cutter sought greater scintillation by making the number of mid-level pavilion facets an odd number rather than the standard even number of facets (Elbe (U.S. Pat. No. 3,788,097).
These attempts to increase the value and beauty of the brilliant-cut diamond have met with varying degrees of success, but there are always new brilliant cuts being developed and experimented with in order to improve the features of brilliance, dispersion, and scintillation. Similarly, in the relatively new field of princess cut diamonds, princess cuts need to be developed which uniquely maximize and balance the features of brilliance, dispersion, and scintillation of the princess cut diamond. Although very broad ranges of certain diamond characteristics have been recognized in the field of princess cut diamonds, there is the need to find the right combination of the various attributes (the number and shape of pavilion and crown facets, the various characteristic percentages, etc.) to uniquely bring forth the brilliance, dispersion, and scintillation of the diamond.
One object of the present invention is to provide a new and unique princess cut gemstone which maximizes and balances the features of brilliance, dispersion, and scintillation of a gemstone.
Another object of the present invention is to provide a princess cut gemstone with an increased number of facets (in comparison to the typical princess cut) to increase the brilliance, dispersion, and scintillation of the gemstone.
Yet another object of the present invention is to provide a novel combination of the various gemstone attributes (the number and shape of pavilion and crown facets, the characteristic percentages, etc.) to uniquely bring forth the brilliance, dispersion, and scintillation of the gemstone.
These and other objects are achieved by a princess cut gemstone according to the present invention. The novel princess cut gemstone comprises a crown, a girdle, and a pavilion. In the presently preferred embodiment, the crown comprises 8 side crown facets, 24 star crown facets, and a table facet. The pavilion comprises 20 side pavilion facets and 44 star pavilion facets. The girdle comprises 4 girdle facets.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.